Contents lists available at ScienceDirect

Hydrometallurgy

journal homepage: www.elsevier.com/locate/hydromet

Recovery of molybdenum from leach solution using polyelectrolyteextraction

Hossein Shalchian⁎, Francesco Ferella, Ionela Birloaga, Ida De Michelis, Francesco VegliòDepartment of Industrial Engineering, Information and Economics, University of L'Aquila, Monteluco di Roio, 67100 L'Aquila, Italy

A R T I C L E I N F O

Keywords:MolybdenumLeaching solutionPolyelectrolyte extractionPurificationSynthesis of layered MoO3

A B S T R A C T

In this research, extraction and purification of molybdenum from a leach solution of molybdenite dissolution wasperformed. Cationic polyelectrolytes were used for the first time in this study for selective recovery of mo-lybdenum. For this purpose, some water-soluble coagulants of KlarAid PC products were employed and theexperimental results in terms of recovery percentages, optimum value of needed polyelectrolyte and theirperformance were investigated. In order to evaluate the extraction and purification process, the precipitatedmolybdenum compounds were studied by ICP-OES, XRD, FTIR, and SEM. The results showed that about 88% ofmolybdenum could be recovered in one step with a final estimated purity of 100%. Afterward, a relatively pureMoO3 product with a layered-structure was successfully synthesized by a simple heat treatment. Finally, theresults showed that the proposed novel method, polyelectrolyte extraction (PX), could be an efficient alternativeto other processes (i.e. ion exchange resins and solvent extraction) for selective recovery of metals from acidsolution.

1. Introduction

Molybdenum is a strategic metal which is widely used in industrialprocesses. It is an important alloying element especially in steels, pro-ducing corrosion resistance and excellent toughness and strength athigh temperatures which makes it suitable for use in aircraft engines. Itis also used in pigments, lubricants, and catalysts. Molybdenum com-pounds are important components of catalysts in a variety of industriessuch as oil and petroleum refining, polymers, plastics and resins makingand alcohol synthesis (Ghiasvand et al., 2005; Park et al., 2010; Sebeniket al., 2002; Valdés et al., 2009).

Molybdenum is extracted usually from molybdenite, the mostcommon mineral of molybdenum in nature which is associated withcopper porphyry ores(Basualto et al., 2003). Selective flotation is aprevalent way to separate molybdenite from copper and iron sulfides.However, as Cu and Fe are always present as impurities in the finalconcentrate, it is very difficult to further use molybdenum product.Therefore, such impurities must be removed from molybdenum. Thereare some procedures to reduce impurity contents of molybdenumcompounds. A major and primary way of molybdenite processing isroasting the sulfide concentrate to produce molybdenum trioxide, themost common precursor for other molybdenum compounds production.In the roasting process, all the impurities are also oxidized. Impuremolybdenum trioxide can be treated by evaporation purification or by

acid washing to remove most of these impurities. In the latter case,some of molybdenum is also dissolved in acidic solution which shouldbe separated. It should be noted that roasting is a high-temperatureprocess, consuming a high amount of energy and producing en-vironmentally harmful sulfur oxides. Hence, many researchers havetried to treat molybdenite concentrate through a hydrometallurgicalroute (Abdollahi et al., 2013; Antonijević and Pacović, 1992; Ashraf,2011; Cao et al., 2009; Jiang et al., 2012; Jianrong et al., 2007;Kholmogorov et al., 2002; Khoshnevisan et al., 2012; Mirvaliev andInoue, 2001; Olson and Clark, 2008; Vizsolyi and Peters, 1980). Theleaching process brings molybdenum and impurities to the solution(leach liquor). Hence, as in the case of acid washing liquor of mo-lybdenum trioxide, a separation and purification treatment is required.

There are many routine separation methods in hydrometallurgy.These methods have also been employed for molybdenum recoveryfrom solutions, including chemical precipitation usually with pH ad-justment and cementation (Li et al., 2012a; Park et al., 2006b; Van denBerg et al., 2002; Warren and Reid, 1982; Zhao et al., 2011), metal ionadsorption on activated carbon surface (Juneja et al., 1996; Kar et al.,2004; Pagnanelli et al., 2011; Park et al., 2006a; Seo et al., 2012), ion-exchange by resins (Fu et al., 2018; Kononova et al., 2003; Nguyen andLee, 2013; Orrego et al., 2019; Padh et al., 2019; Zhao et al., 2010),supported liquid membrane separation (Basualto et al., 2003; Chaudryet al., 1990; Marchese et al., 2004) and solvent extraction by organic

https://doi.org/10.1016/j.hydromet.2019.105167Received 22 June 2019; Received in revised form 23 September 2019; Accepted 4 October 2019

⁎ Corresponding author.E-mail address: hsh.metal@gmail.com (H. Shalchian).

Hydrometallurgy 190 (2019) 105167

Available online 16 October 20190304-386X/ © 2019 Elsevier B.V. All rights reserved.

T

solvents (Alamdari et al., 2012; An et al., 2009; Gerhardt et al., 2001;Imam and El-Nadi, 2018; Noronha et al., 2013; Park et al., 2010; Satoet al., 1990; Wang et al., 2014; Wu et al., 2012; Zhu et al., 2015).Precipitation is considered as being the simplest (it does not requirespecial equipment), most inexpensive and relatively fast process.However, the final product is impure and needs further purificationsteps. Carbon adsorption is not effective due to its small capacity, lowselectivity, time-consuming and more complex procedure. The ion ex-change method is the same as the carbon adsorption process, but it ismore selective and more expensive. Hence, these two methods arerarely employed in practice (Alamdari et al., 2012; Wu et al., 2012).Supported liquid membrane separation is more effective but has rareapplications in industrial scale due to its disadvantages such as capitalcost and membrane instability in terms of long time performance (Maliket al., 2011; Parhi, 2012). Solvent extraction is a more effective andapplicable technique for separation and purification in industrialpractices and many types of research have been conducted in this field(Alamdari et al., 2012; An et al., 2009; Gerhardt et al., 2001; Imam andEl-Nadi, 2018; Noronha et al., 2013; Park et al., 2010; Sato et al., 1990;Wang et al., 2014; Wu et al., 2012; Zhu et al., 2015). As in the case ofother technologies, this method presents advantages and disadvantages.

The operation and equipment are relatively simple and components arerecyclable, production capacity is larger than the one achieved bycarbon adsorption or ion exchange with resins, and the process leads tohigh purity final product (Li et al., 2012b). Solvent extraction is con-sidered as a more versatile method for removal of metallic ion im-purities. However, it presents serious limitations including expensivesolvents, large volume of solvents, different kinds of chemical com-pounds such as diluting solvents, organic extractants, modifiers andstripping agents, high operation costs, large equipment (several mixer-settler system), high residence time, possible formation of emulsions,crud formation at interphase and phase entrainment difficulties andsometimes due to its low content of molybdenum in waste leach solu-tions, the SX process in conventional mixer-settler reactors becomeseconomically inapplicable(Basualto et al., 2003; Valdés et al., 2009).

In the present study, the results of a new process for separation andrecovery of molybdenum from solution is present. It involves the use ofsoluble polymers (polyelectrolytes) that have found applications forsolid-liquid separation in a variety of industries such as papermaking,water treatment and mineral processing. They also have some appli-cations in drug delivery, food sciences, cosmetics and fabrication ofnanofilms and nanostructures (Frueh et al., 2014; Liu et al., 2017;

Table 1A comparison of already existing processes on Mo recovery and the novel method proposed in this study (Polyelectrolyte extraction).

Method Main advantages Main disadvantages

Chemical precipitation (Li et al., 2012a; Park et al., 2006b; Vanden Berg et al., 2002; Warren and Reid, 1982; Zhao et al.,2011)

• Very simple process

• Inexpensive

• Without any special equipmentrequirement

• Relatively fast method

• Impure final product

• Needs more purification processes

• Needs different chemical agents for pH adjustment or reductive/oxidative treatment

Metal ion adsorption on activated carbon surface (Juneja et al.,1996; Kar et al., 2004; Pagnanelli et al., 2011; Park et al.,2006a; Seo et al., 2012)

• Relatively inexpensive process

• Relatively simple equipment• Small capacity

• Low selectivity

• Time consuming process

• Relatively complex processIon-exchange by resins (Fu et al., 2018; Kononova et al., 2003;

Nguyen and Lee, 2013; Orrego et al., 2019; Padh et al., 2019;Zhao et al., 2010)

• More selective than the carbonadsorption process

• Relatively simple operation andequipment

• Recyclable component

• Relatively expensive

• Small capacity

• Time consuming process

Solvent extraction by organic solvents (Alamdari et al., 2012; Anet al., 2009; Gerhardt et al., 2001; Imam and El-Nadi, 2018;Li et al., 2012b; Noronha et al., 2013; Park et al., 2010; Satoet al., 1990; Wang et al., 2014; Wu et al., 2012; Zhu et al.,2015)

• More effective

• More applicable

• Selective

• Relatively simple operation andequipment

• Recyclable component

• More production capacity

• High purity final product

• Expensive solvents with huge inventories

• Large volume of solvents

• Different kinds of chemical compounds (diluting solvents,organic extractants, modifiers and stripping agents)

• High operation costs

• Large equipment (several mixer-settler system)

• High residence time

• Possible formation of emulsions

• Crud formation at interphase

• Sometimes inapplicable economically, for waste leach solutionswith low content of molybdenum

Supported liquid membrane separation (Basualto et al., 2003;Chaudry et al., 1990; Malik et al., 2011; Marchese et al.,2004; Parhi, 2012)

• High selectivity

• Combine extraction and strippinginto one single stage

• No limitation by the conditions ofequilibrium (Uphill TransportCharacteristic)

• More efficient process due to highInterfacial area per unit volume

• Smaller equipment than classicalsolvent extraction systems

• Rare industrial application due to membrane instability (leadsto the reduction of solute flux and membrane selectivity)

• Membrane resistance to mass transfer (more operation time)

• Lack of research

Polyelectrolyte extraction • Very simple process

• Inexpensive

• Without any special equipmentrequirement

• Relatively fast method

• High purity final product

• Simple phase separation

• No need to inorganic materials anddifferent chemicals

• Very low operation cost

• Applicable even for solutions withlow content of molybdenum

• Only applicable for recovery and purification purposes in thesolutions containing target element as anion and impurities ascations and vice versa (using cationic or anionicpolyelectrolytes)

H. Shalchian, et al. Hydrometallurgy 190 (2019) 105167

2

Petzold and Schwarz, 2013). Surface charge neutralization of solidparticles by using these polymers can produce large flocs that can beeasily separated/recovered. Polyelectrolytes are polymers whosemonomer groups bear a charge that can dissociate into a chargedmacro-ion and small counter-ion when it is dissolved in a polar solventand make the solvent electrically neutral but conductive (Frueh et al.,2014). There are two kinds of polyelectrolytes based on the charge ofmacroions which can be positive or negative and called polycations andpolyanions, respectively. In fact, the monomer macro-ions (positive ornegative) can interact with the surface of charged particles (negative orpositive) in polar solvents and produce flocs to make an efficient solid-liquid separation.

As mentioned above, these polyelectrolytes are mainly used in se-dimentation of solid particles, but they have never been used in mo-lybdenum hydrometallurgy. According to the results of this study, whenthis water soluble extractant is used, high purity solid product con-taining metal ion can be precipitated. Then, the high purity solid par-ticles are easily separated by filtration. The method is similar to generalprecipitation but does not need pH adjustment or addition of inorganicmaterials that can considerably affect the purity of precipitated parti-cles. This will be an ideal process to metal ion recovery from theleaching solution due to very simple equipment. The only neededequipment is a mixing and filtration system, instead of a large numberof devices required for solvent extraction process (i.e. mixer-settlersystems and columns for countercurrent extraction. In addition, thestripping stage from pregnant phase will be completely omitted.

It should be noted that polyelectrolytes have also been used to re-move heavy metal ions from aqueous solutions of wastewaters. In thesecases, heavy metal binding with a chemical agent was initially allowedto occur and then the polyelectrolyte was added to initiate the complexprecipitation (Hankins et al., 2006; Navarro et al., 2005). The labora-tory results of the present study demonstrates for the first time thatmolybdenum can be selectively precipitated from leach liquor by usinga cationic polyelectrolyte (CPE) without any additive or auxiliary agentfor the complex formation or even pH adjustment.

So, this paper reports a novel method for simultaneous selectiverecovery and purification of molybdenum from leach liquor in one step.

A comparison of main advantages and disadvantages of already existingprocesses on Mo recovery and the polyelectrolyte extraction is shown inTable 1.

2. Materials and methods

The initial solution for purification experiments was prepared bydissolving some molybdenite (MoS2) concentrate in nitric acid media.Molybdenite concentrate (55.6% Mo, 0.58% Cu and 0.96% Fe) wassupplied by Sarcheshmeh Copper Complex (Iran). The residual super-ficial organic compound of the concentrate was removed based on aprocess that has been reported elsewhere (Shalchian et al., 2018;Shalchian et al., 2017). Mechanical activation was performed for 4 hbefore leaching to improve dissolution efficiency of molybdenite con-centrate (Shalchian et al., 2018).

The leaching experiment was performed for 3 h in a 0.2M nitric acidsolution using a cylindrical water jacketed vessel (borosilicate glass, 1 l)under magnetic stirring (500 rpm). A digital bath with a circulatingpump (CRIOTERM 10–80 Thermostat) was used to control the tem-perature at 78 °C (Shalchian et al., 2018).

The most probable reaction for nitric acid leaching of molybdeniteis as follows (Vizsolyi and Peters, 1980):

+ → + + + −MoS 6HNO MoO ·nH O 2 H SO 6 NO (1 n) H O2 3 3 2 2 4 2 (1)

Solid to liquid ratio of 1.3 g/l was selected to prevent saturation ofmolybdenum in solution (Shalchian et al., 2018; Vizsolyi and Peters,1980). The separation of solid and liquid phases was performed using avacuum filter and the concentration of Mo, Cu and Fe in the final so-lution was determined by ICP-OES.

For molybdenum extraction, several CPE water-soluble coagulantsof KlarAid products (KlarAid PC 1182, KlarAid PC 1192, KlarAid PC1194, KlarAid PC 1195, KlarAid PC 1196 and KlarAid PC 2712) wereemployed. The purification experiments have been performed byadding specified amounts of CPE to the initial solution. Their additionhave determined the coagulation/precipitation of molybdenum ions. Avacuum filter was used after each experiment to separate the solid fromthe liquid phase. Filter cake underwent a washing step using distilledwater and finally, it was dried at 105 °C for 6 h. Molybdenum, copper

Fig. 1. Coagulation of Mo ions in measuring cylinders by adding different values of KlarAid PC 1192 to the leach liquor for determining the maximum allowedconcentration of CPE, with corresponding recovery percentages of Mo, Cu, and Fe.

H. Shalchian, et al. Hydrometallurgy 190 (2019) 105167

3

and iron content of the solutions were analyzed by an InductivelyCoupled Plasma spectrophotometer (ICP-OES 5100 AgilentTechnologies) and recovery efficiency was calculated by mass balance.The dried precipitates were analyzed by a Fourier transform infraredspectrometer (FT-IR, Thermo Nicolet) with KBr pellet technique in therange of 400–4000 cm−1. Thermal treatment and analysis were per-formed using a LINSEIS STA PT 1600 instrument at a heating rate of10 °C/min from ambient temperature to 750 °C. Furthermore, theachieved powders (before and after thermal treatment) were

characterized by XRD analysis using a Philips Panalytical instrumentwith Cu anode material and K-Alpha radiation (λ=0.154060 nm). TheX-ray diffraction patterns were measured in 2θ range of 10–90°.Scanning electron microscopy (SEM) observations were performedusing a Philips microscope operating at 20 kV. It should be noted thatOrigin (OriginLab, Northampton, MA) was used for graph drawing andChemDraw was employed for schematic drawing.

Fig. 2. Recovery percentages of Mo, Cu, and Fe from leach liquor using different CLPE: (a) KlarAid PC 1182, (b) KlarAid PC 1192, (c) KlarAid PC 1194, (d) KlarAid PC1195, (e) KlarAid PC 1196 and (f) KlarAid PC 2712.

H. Shalchian, et al. Hydrometallurgy 190 (2019) 105167

4

3. Results and discussion

3.1. Precipitation experiments

ICP analysis showed that Mo, Cu and Fe content of as-received leachliquor is 615.3, 7.4 and 15.7mg/L, respectively. Hence, molybdenumcontent is 96.4 wt%, considering the three elements concentration. Ironand copper sulfides dissolve as cations while molybdenite dissolution innitric acid resulted in the formation of molybdic acid producingMoO42− anions (Vizsolyi and Peters, 1980).

In order to investigate the effect of CPE on the extraction and pur-ification of molybdenum ions from solution, some experiments wereperformed at different values of CPE. For instance, Fig. 1 shows theeffect of KlarAid PC 1192 vol% on the precipitation behavior and re-covery of Mo, Fe, and Cu. In these experiments, a 5% solution wasprepared by dissolving CPE in distilled water. The diluted solution wasadded to the leach liquor in 2–10 vol% of the total volume. As can beseen, at the early stages, the precipitate volume and recovery percen-tage of molybdenum increases simultaneously with increasing the CPEvalue (Fig. 1). By exceeding the 7.2 vol%, phase separation encountersa problem. In fact, the sharp solid/liquid interface is destroyed andsome of the solid particles are not precipitated which makes somedifficulties in subsequent filtration step.

According to the results of Fig. 1, it is obvious that from one handthere is a threshold for the concentration of CPE in solution in which,phase separation is not possible at higher values of coagulant. On theother hand, the recovery percentage of molybdenum is low at lowervalues of CPE. Therefore, the maximum usable value of CPE should bedetermined in experiments. So, it is necessary to specify the allowablerange of coagulants concentration at the first step, which was obtained

by some experiments. Subsequently, the effect of CPE values on therecovery of Mo, Cu, and Fe was investigated and the results are shownin Fig. 2. As can be seen, the recovery of Fe and Cu is very low for allCPEs, indicating a selective separation of Mo from solution (Fig. 2). Itshould be noted that the recovery percentages of Mo, Cu, and Fe pre-sented in Fig. 2 are calculated by the mass balance between the contentof all three elements within the initial solution, depleted solution afterfiltration and wash water of the filter cake at one step of extraction.

Fig. 2 reveals that there are three behaviors based on used CPEvalues and Mo extraction. In type 1, Mo extraction increases linearlyproportional to increment of CPE vol% up to the threshold limit.KlarAid PC 1182 is an example of this type. For the second type, Moextraction improves by increasing coagulant value, but it reduces gra-dually. CPE of KlarAid PC 1192, KlarAid PC 1196 and KlarAid PC 2712are categorized in type 2. Finally, the Mo extraction is independent ofCPE value in type 3. The recovery percentage of Mo ions using KlarAidPC 1194 is almost the same at different vol% of CPE solution (Fig. 2).Therefore, it belongs to type 3. Considering the above explanations,KlarAid PC 1195 can be categorized either in type 2 and type 3.

The suitable value of CPE is the lowest level which leads to Morecovery as high as possible in one step of extraction. Therefore, con-sidering the linear relation of Mo recovery versus CPE value (17.5 vol%for KlarAid PC 1182 in Fig. 2) in type 1, the maximum vol% of CPEbefore the threshold limit of phase separation can be chosen. On theother hand, in type 2, the optimum value of CPE is somewhere betweeninitial and threshold limit, in which the recovery rate of molybdenumdecreases. It is obviously that the lowest value of CPE is acceptable intype 3, due to the independence of Mo recovery by CPE vol% (Fig. 2).

As claimed by Fig. 2, the highest value of Mo recovery in one step isobtained using KlarAid PC 1192, KlarAid PC 1194 and KlarAid PC1195. The lowest value of Mo recovery belongs to KlarAid PC 2712which is a type 2 member. In addition, the Fig. 2 shows that the highest

Fig. 3. Calculated Efficiency factor versus CPE values using data in Fig. 2 forKlarAid PC 1182, KlarAid PC 1192, KlarAid PC 1194, KlarAid PC 1195, KlarAidPC 1196 and KlarAid PC 2712.

Table 2Extracted Mo values from the solutions and removal percentage of Cu and Fe, before and after the washing treatment.

KlarAid PC Polyelectrolyte value (Vol%)

Before washing of precipitates After washing of precipitates Estimated purity of finalproduct (%)

Mo extraction(%)

Cu removal(%)

Fe removal(%)

Mo extraction(%)

Cu removal(%)

Fe removal(%)

1182 12.5 61.4 98.9 98.9 60.2 100 100 1001192 6.4 81.9 97.6 98.2 81.5 98.6 99.2 99.951194 2 87.5 99.3 99.2 86.9 100 100 1001195 4 88.5 98.1 98.9 88.1 100 100 1001196 6 75.7 96.3 96.6 75.2 97.7 97.9 99.892712 6.4 37 97 97 35.7 98.4 98.3 99.83

Fig. 4. Effect of type of cationic polyelectrolyte on the rate of precipitation andphase separation, considering interface movement.

H. Shalchian, et al. Hydrometallurgy 190 (2019) 105167

5

usage of CPE is related to KlarAid PC 1182. 17.5 vol% of a 10% solutionis used to recover only 69% of molybdenum ions, while similar re-covery degrees of Mo have been achieved with lower volumes of 5% ofthe others 5 CPEs.

In order to investigate the performance of CPEs, the efficiency factoris quantitatively defined. The aforementioned parameter is obtained bydividing molybdenum recovery to the used value of CPE. In fact, theefficiency factor expresses the recovered Mo (grams) per unit volume ofCPE (liter) as follows:

=×

×

×Efficiency factor C RP D

11000g l( / )Mo CPE (2)

where C is Mo concentration of leach liquor in mg/L, R represents therecovery percentage of molybdenum, P is equal to CPE quantity (vol%),and D is dilution percentage of CPE solution (%) which is considered5% and 10% in this study.

Fig. 3 shows the calculated efficiency factor for 6 used CPEs ac-cording to the data of Fig. 2. It is clear that the efficiency factor forKlarAid PC 1182 and KlarAid PC 2712 has the lowest value (less than100 g per liter of CPE). Fig. 3 reveals also that the efficiency factordecreases by increasing CPE quantity. In other words, the incrementrate of Mo extraction is less than the increasing rate of CPE quantity. Inthe case of an equality of two of the aforementioned rates, it is expectedthat the slope of the graph tends to zero value and at a reverse situation,when the rate of Mo extraction is higher than the increasing rate of CPEquantity, efficiency factor increases.

Concerning Fig. 3, the maximum value of efficiency factor belongsto KlarAid PC 1194 which decreases by the addition of more CPE up to4 vol%. Based on the above explanations, KlarAid PC 1194 is a memberof type 3 with the independence of recovery percentage to CPE quantityand Mo recovery is almost constant in the whole range of studied CPEvalues. So, regarding to Eq. (2), efficiency factor decreases by a con-stant numerator and increasing denominator.

Fig. 3 also disclosure another point about the behavior of CPEs. Asdiscussed earlier, KlarAid PC 1195 could be categorized either in type 2and type 3, but Fig. 3 shows its similar trend to KlarAid PC 1194.Therefore, it can be said KlarAid PC 1195 belongs to type 3 of CPEs.

The obtained precipitates after coagulation and filtration were wa-shed using distilled water which improved the purity of the product byremoving more Cu and Fe ions. Table 2 represents the recovery per-centages of Mo, Cu, and Fe before and after washing step. The estimatedpurity of the final product was also calculated by mass balance.

It is evident that the purity increased, especially for KlarAid PC1182, KlarAid PC 1194 and KlarAid PC 1195 with complete removal ofCu and Fe impurities (Table 2). It seems that the low values of un-desirable elements in precipitates before washing are trapped duringcoagulation and can easily be removed by washing. Therefore, the re-sults have shown that CPE is an efficient extraction and purificationagent for molybdenum.

In the coagulation process, the rate of phase separation and sedi-mentation is different for various kinds of CPEs. Naturally, at a faster

Fig. 5. FTIR analysis of cationic polyelectrolytes and relevant precipitates after drying.

Fig. 6. XRD patterns of precipitates after drying.

H. Shalchian, et al. Hydrometallurgy 190 (2019) 105167

6

rate of solid/liquid phase separation, the process is simpler, time-savingand consequently more economic. Therefore, the aforementionedparameter was studied for different CPEs (Fig. 4). The rate of phaseseparation was plotted by measuring the movement of solid/liquid in-terface versus time in cylinder. As it can be seen, the interface reachesto 30ml in 90min in the case of KlarAid PC 1194. Fig. 4 also shows thatthe lowest rate of precipitation belongs to KlarAid PC 1182 and thehighest one is related to KlarAid PC 1196 and KlarAid PC 2712.

3.2. Characterization of precipitates

Fig. 5 illustrates FTIR spectrums of different CPEs and related pre-cipitates after the coagulation process. As can be seen, there is a wideabsorption between 3000 and 4000 cm−1 in all cases corresponding to–OH bonds of water molecules of as-received CPEs solutions. Con-sidering FTIR analysis of CPEs before adding to leach liquors and afterprecipitation, relatively complex spectra are obtained after the coagu-lation process for 6 kinds of CPEs. So, almost all of the added

Fig. 7. Scanning electron microscopy images of obtained precipitates by using cationic polyelectrolytes: (a)KlarAid PC 1182, (b) KlarAid PC 1192, (c) KlarAid PC1194, (d) KlarAid PC 1195, (e) KlarAid PC 1196, (f) KlarAid PC 2712.

Fig. 8. TGA-DTA graph of obtained dried precipitates by using cationic polyelectrolytes: (a)KlarAid PC 1182, (b) KlarAid PC 1192, (c) KlarAid PC 1194, (d) KlarAidPC 1195, (e) KlarAid PC 1196, (f) KlarAid PC 2712.

H. Shalchian, et al. Hydrometallurgy 190 (2019) 105167

7

absorptions before 2000 cm−1 are related to extracted Mo ions bypolyelectrolytes. For example, related bands of MoeO bonding presentat the range of 700–950 (cm−1) (Carrazan et al., 1996) reveals theabsorption of [MoO4]2− by CPEs.

XRD patterns of dried precipitates after the coagulation process areshown in Fig. 6. There is the same pattern for all 6 kinds of CPEs,showing the same crystallographic nature for all samples. It is clear thatthere is not any specific peak of crystalline phases. In other words, theobtained product after drying is a non-crystalline material with glassycharacteristics. It should be noted the appearance of the dried filtercake of precipitates has also a glassy shape (not shown here), which isin accordance with XRD patterns.

In order to get more details, all samples were evaluated by scanningelectron microscopy. Fig. 7 shows SEM images of obtained precipitatesby adding 6 different kinds of CPEs to the leach liquor after drying. Canbe seen that the particles in all images are similar in shape. A notablepoint of Fig. 7 is a seashell-like fracture pattern of particles which is

evident especially in Fig. 7 (a), (b) and (d). The aforementioned patternis a consequence of brittle fracture of particles. It should be mentionedthat, in order to obtain a fine powder, the coarse dried and glassyparticles of precipitates were ground before XRD and SEM analysis. So,it seems that the grinding process resulted in such a fracture. XRDanalysis, on the other hand, revealed that the obtained precipitatesconsist of an amorphous and glassy phase (Fig. 6). Therefore, the sea-shell-like pattern is observed during fracture phenomena of the brittleglassy particles. Fig. 7 (e) shows a crack without plastic deformationalso illustrating somewhat the brittle nature of the particles.

3.3. Synthesis of MoO3

Fig. 8 shows the results of thermal analysis for 6 dried precipitatesusing various CPEs. The organic constituents of cationic polyelec-trolytes are dissociated during heating. Negative mass changes andrelated peaks in DTA analysis correspond to outgoing of materials indifferent temperatures leaving behind inorganics. The aforementionedphenomena resulted in about 50% mass reduction in different samples.Most of the mass reduction and related DTA peaks occurred at the rangeof 200–600 °C for all the dried precipitates. It should be noted thehighest value of mass reduction belongs to KlarAid PC 1182, which is inaccordance with the highest value of used polyelectrolyte in the coa-gulation process (Fig. 2).

The residual constituents after thermal treatment using DTA-TGAanalysis were evaluated by X-ray diffraction. Fig. 9 shows XRD patternsof obtained precipitates. It is clear that amorphous phases beforethermal analysis (Fig. 6) are crystallized during heating up to 750 °Cleading to the formation of MoO3 crystals (Fig. 9). For KlarAid PC 1194,it seems that the transformation is not completed yet, needing moretemperatures. So, it can be said that thermal treatment is useful toevaporate organic components and formation of relatively pure Mo-lybdenum trioxide (Table 2). The pure MoO3 crystals in Fig. 9 are alsoin accordance with the estimated purity of the final product in Table 2.

The obtained MoO3 particles were further investigated using SEM.Fig. 10 illustrates electron microscopy images of the final products of 6precipitates after thermal treatment. Crystalline nature of particles is

Fig. 9. XRD patterns of precipitates after thermal treatment.

Fig. 10. Scanning electron microscopy images of precipitates after thermal treatment by using cationic polyelectrolytes: (a) KlarAid PC 1182, (b) KlarAid PC 1192,(c) KlarAid PC 1194, (d) KlarAid PC 1195, (e) KlarAid PC 1196, (f) KlarAid PC 2712.

H. Shalchian, et al. Hydrometallurgy 190 (2019) 105167

8

clearly evident in comparison to the initial precipitates before thermaltreatment (Fig. 7) which confirms the crystallization of MoO3 fromamorphous and glassy particles. These results are in accordance withthe XRD analysis. A noticeable point is the synthesis of MoO3 crystalswith long ordered layered-structure is achieved by this procedure.Considering the increasing importance of two-dimensional materialsnowadays, it is easy to achieve nanometric layers of MoO3 by differentknown methods of exfoliation, which are very useful in nanoscienceand technology (Chen et al., 2018; Etman et al., 2018; Liu et al., 2018;Sharma et al., 2018; Su et al., 2019; Zhong et al., 2018). Therefore, inaddition to extraction and purification of Mo in leach liquor, pure MoO3

crystals with layered-structure were synthesized directly, using cationicpolyelectrolytes coagulation followed by a thermal treatment.

4. Concluding remarks

In this research, the effectiveness of cationic polyelectrolytes inselective precipitation and purification of Mo ions from leach liquorcontaining Fe and Cu was proven. The mechanism of coagulation of Moions can be expressed based on the charged nature of ions and poly-electrolytes in solution. From a theoretical point of view, positively-charged molecules would be able to attract anions and repel cations.Cationic polyelectrolytes on the other hands forms positively chargedmolecules by ionization in water. So, they would be able to selectivelyattract anions of molybdenum ([MoO4]2−) by counter-ion binding andreduce the barrier against coagulation due to the electroneutralityphenomenon. Therefore, Mo ions are aggregated with positive mole-cules of polyelectrolytes and Fe and Cu cations are repelled to the so-lution as impurities. Consequently, purification of Mo ions occurredsimultaneously, in addition to molybdenum recovery from leach liquor.A schematic of the process is illustrated in Fig. 11 using poly (dia-llyldimethylammonium chloride) solution. The results of Table 2 con-firmed that cationic polyelectrolytes only coagulate Mo anions. It seemsthat a few amounts of Fe and Cu cations are trapped during coagulationbecause a simple water washing reduced their concentration sig-nificantly.

A remarkable point is the simplicity of the proposed method. So thatcoagulation occurs as soon as polyelectrolytes are added to the solution

and molybdenum ions are precipitated in the form of small flakes.Therefore, it is possible to separate the solid phase quickly, by a simplefiltration step. A glassy and amorphous phase is obtained by drying thefilter cake which is transformed into layered crystals of pure MoO3

through thermal treatment. Accordingly, synthesis of pure MoO3 crys-tals is the other impressive feature of the proposed process which can beused to produce few-layers or even mono-layers of MoO3 during anappropriate exfoliation process. Therefore, considering the benefits ofthe proposed method, it would be more effective for processing mo-lybdenum leach liquors than to perform the common extractionmethods such as solvent extraction and ion exchange using resins.Finally, it should be said that the aforementioned method could be usedfor extraction and purification of other metal ions by appropriate se-lection of cationic or anionic polyelectrolytes for anions and cations,respectively.

5. Summary

In summary, we investigated the extraction and purification ofmolybdenum from a leach liquor containing iron and copper ions asimpurities using some cationic polyelectrolytes for the first time. Theoutstanding results are as follows:

• recovery and purification of Mo from Fe and Cu ions was performedby using relatively low values of polyelectrolytes concentration in asingle step;

• there is an optimum concentration for any polyelectrolytes. Therecovery percentage of molybdenum is low at lower values of ca-tionic polyelectrolytes. On the other hands, phase separation is notpossible at values higher than the threshold concentration;

• in order to investigate the recovery efficiency of precipitated mo-lybdenum based on used polyelectrolyte, the efficiency factor wasdefined. The aforementioned parameter was used to evaluate theperformance of polyelectrolytes;

• using of various polyelectrolytes led to different rates of coagulationand precipitation, ranging from 10min to more than 200min inexperimental conditions;

• for cationic polyelectrolytes of KlarAid PC 1194 and KlarAid PC

Fig. 11. A schematic of molybdenum recovery and purification from leach liquor using a cationic polyelectrolyte.

H. Shalchian, et al. Hydrometallurgy 190 (2019) 105167

9

1195, the best conditions of Mo extraction and purification wereobtained. The highest value of the efficiency factor with an esti-mated purity of 100% and a mid-range rate of precipitation wereachieved in both cases;

• XRD and SEM investigations showed that a glassy and amorphousphase is obtained after drying of coagulants. Finally, relatively pureMoO3 layered-crystals were synthesized by heating the precipitatesup to 750 °C.

Funding

This research did not receive any specific grant from fundingagencies in the public, commercial, or not-for-profit sectors.

Declaration of Competing Interest

None.

Acknowledgment

Authors kindly acknowledge Mr. Marcello Centofanti for the ICPanalyses, and Sarcheshmeh Copper Complex for supplying the mo-lybdenite concentrate.

References

Abdollahi, H., Shafaei, S., Noaparast, M., Manafi, Z., Aslan, N., 2013. Bio-dissolution ofCu, Mo and Re from molybdenite concentrate using mix mesophilic microorganism inshake flask. Trans. Nonferrous Metals Soc. China 23 (1), 219–230.

Alamdari, E.K., Darvishi, D., Haghshenas, D., Yousefi, N., Sadrnezhaad, S., 2012.Separation of Re and Mo from roasting-dust leach-liquor using solvent extractiontechnique by TBP. Sep. Purif. Technol. 86, 143–148.

An, J., et al., 2009. Production of high purity molybdenum compounds from a Cu–Moacid-washed liquor using solvent extraction. Part 1: laboratory studies. Miner. Eng.22 (12), 1020–1025.

Antonijević, M., Pacović, N., 1992. Investigation of molybdenite oxidation by sodiumdichromate. Miner. Eng. 5 (2), 223–233.

Ashraf, M., 2011. Hydrometallurgical recovery of molybdenum from Egyptian Qattarmolybdenite concentrate. Physicochem. Probl. Miner. Process 47, 105–112.

Basualto, C., Marchese, J., Valenzuela, F., Acosta, A., 2003. Extraction of molybdenum bya supported liquid membrane method. Talanta 59 (5), 999–1007.

Cao, Z.-f., Zhong, H., Qiu, Z.-h., Liu, G.-y., Zhang, W.-x., 2009. A novel technology formolybdenum extraction from molybdenite concentrate. Hydrometallurgy 99 (1), 2–6.

Carrazan, S., Martin, C., Rives, V., Vidal, R., 1996. An FT-IR spectroscopy study of theadsorption and oxidation of propene on multiphase Bi, Mo and Co catalysts.Spectrochim. Acta A Mol. Biomol. Spectrosc. 52 (9), 1107–1118.

Chaudry, M.A., Malik, M.T., Ali, A., 1990. Transport of Mo (VI) ions through tri-n-octy-lamine-xylene based supported liquid membranes. Sep. Sci. Technol. 25 (3),263–291.

Chen, Q., et al., 2018. Rapid preparation of large size, few-layered MoO3 by anisotropicetching. Mater. Lett. 229, 305–307.

Etman, A., Wang, L., Nyholm, L., Edström, K., Sun, J., 2018. One-Pot Synthesis of MoO3-xNanosheets for Supercapacitor Applications, the E-MRS 2018 Spring Meeting, June18 to 22. Strasbourg, France.

Frueh, J., Gai, M., Halstead, S., He, Q., 2014. Structure and Thermodynamics ofPolyelectrolyte Complexes, Polyelectrolytes. Springer, pp. 19–86.

Fu, Y., et al., 2018. Direct extraction of Mo (VI) from acidic leach solution of molybdeniteore by ion exchange resin: batch and column adsorption studies. Trans. NonferrousMetals Soc. China 28 (8), 1660–1669.

Gerhardt, N.I., Palant, A., Petrova, V., Tagirov, R., 2001. Solvent extraction of mo-lybdenum (VI), tungsten (VI) and rhenium (VII) by diisododecylamine from leachliquors. Hydrometallurgy 60 (1), 1–5.

Ghiasvand, A., Shadabi, S., Mohagheghzadeh, E., Hashemi, P., 2005. Homogeneous li-quid–liquid extraction method for the selective separation and preconcentration ofultra trace molybdenum. Talanta 66 (4), 912–916.

Hankins, N.P., Lu, N., Hilal, N., 2006. Enhanced removal of heavy metal ions bound tohumic acid by polyelectrolyte flocculation. Sep. Purif. Technol. 51 (1), 48–56.

Imam, D., El-Nadi, Y., 2018. Recovery of molybdenum from alkaline leach solution ofspent hydrotreating catalyst by solvent extraction using methyl tricaprylammoniumhydroxide. Hydrometallurgy 180, 172–179.

Jiang, K., Wang, Y., Zou, X., Zhang, L., Liu, S., 2012. Extraction of molybdenum frommolybdenite concentrates with hydrometallurgical processing. JOM 64 (11),1285–1289.

Jianrong, P., Dajin, Y., Jiaxi, C., Jiangfeng, Y., 2007. Experimental study on alkalineleaching of crude Molybdenite under pressure of oxygen. Chinese J. Rare Metals 31(S1), s110–s113.

Juneja, J., Singh, S., Bose, D., 1996. Investigations on the extraction of molybdenum andrhenium values from low grade molybdenite concentrate. Hydrometallurgy 41 (2),

201–209.Kar, B., Datta, P., Misra, V., 2004. Spent catalyst: secondary source for molybdenum

recovery. Hydrometallurgy 72 (1), 87–92.Kholmogorov, A., et al., 2002. Molybdenum recovery from mineral raw materials by

hydrometallurgical methods. Eur. J. Miner. Process. Environ. Prot. 2 (2), 82–93.Khoshnevisan, A., Yoozbashizadeh, H., Mozammel, M., Sadrnezhaad, S.K., 2012. Kinetics

of pressure oxidative leaching of molybdenite concentrate by nitric acid.Hydrometallurgy 111, 52–57.

Kononova, O., Kholmogorov, A., Kachin, S., Kalyakina, O., Sadovskaya, E., 2003. Ionexchange recovery of molybdenum from nitric acidic solutions using macroporousanion exchangers with long-chained cross-linking agents. Hydrometallurgy 68 (1),83–87.

Li, J., Zhao, Z., Cao, C., Zhang, G., Huo, G., 2012a. Recovery of Mo from Ni–Mo ore leachsolution with carrier co-precipitation method. Int. J. Refract. Met. Hard Mater. 30 (1),180–184.

Li, X., et al., 2012b. Co-extraction and selective stripping of vanadium (IV) and mo-lybdenum (VI) from sulphuric acid solution using 2-ethylhexyl phosphonic acidmono-2-ethylhexyl ester. Sep. Purif. Technol. 86, 64–69.

Liu, X., Chapel, J.-P., Schatz, C., 2017. Structure, thermodynamic and kinetic signaturesof a synthetic polyelectrolyte coacervating system. Adv. Colloid Interf. Sci. 239,178–186.

Liu, H., et al., 2018. Aqueous and mechanical exfoliation, unique properties, and theo-retical understanding of MoO 3 nanosheets made from free-standing α-MoO 3 crys-tals: Raman mode softening and absorption edge blue shift. Nano Res. 11 (3),1193–1203.

Malik, M.A., Hashim, M.A., Nabi, F., 2011. Ionic liquids in supported liquid membranetechnology. Chem. Eng. J. 171 (1), 242–254.

Marchese, J., Valenzuela, F., Basualto, C., Acosta, A., 2004. Transport of molybdenumwith Alamine 336 using supported liquid membrane. Hydrometallurgy 72 (3),309–317.

Mirvaliev, R., Inoue, K., 2001. Pressure oxidation leaching of Molybdenite in alkalinemedia-autoclave processing of low-grade molybdenite concentrates (2ndreport).Sigen-to-Sozai 11, 72–76.

Navarro, R.R., Wada, S., Tatsumi, K., 2005. Heavy metal precipitation by poly-cation–polyanion complex of PEI and its phosphonomethylated derivative. J. Hazard.Mater. 123 (1–3), 203–209.

Nguyen, T.H., Lee, M.S., 2013. Separation of molybdenum and vanadium from acid so-lutions by ion exchange. Hydrometallurgy 136, 65–70.

Noronha, L., Kamble, G., Kolekar, S., Anuse, M.A., 2013. Recovery of molybdenum (VI)from hydrochloric acid medium by solvent extraction with 2-n-octylaminopyridine.Int. J. Chem. Sci. Tech 3, 15–24.

Olson, G.J., Clark, T.R., 2008. Bioleaching of molybdenite. Hydrometallurgy 93 (1),10–15.

Orrego, P., Hernández, J., Reyes, A., 2019. Uranium and molybdenum recovery fromcopper leaching solutions using ion exchange. Hydrometallurgy 184, 116–122.

Padh, B., Rout, P., Mishra, G., Suresh, K., Reddy, B.R., 2019. Recovery of nickel andmolybdate from ammoniacal leach liquors of spent HDS catalysts using chelating ionexchange resin. Hydrometallurgy 184, 88–94.

Pagnanelli, F., Ferella, F., De Michelis, I., Vegliò, F., 2011. Adsorption onto activatedcarbon for molybdenum recovery from leach liquors of exhausted hydrotreatingcatalysts. Hydrometallurgy 110 (1), 67–72.

Parhi, P., 2012. Supported liquid membrane principle and its practices: a short review. J.Chem. 2013.

Park, K.H., Mohapatra, D., Reddy, B.R., 2006a. Selective recovery of molybdenum fromspent HDS catalyst using oxidative soda ash leach/carbon adsorption method. J.Hazard. Mater. 138 (2), 311–316.

Park, K.H., Reddy, B.R., Mohapatra, D., Nam, C.-W., 2006b. Hydrometallurgical proces-sing and recovery of molybdenum trioxide from spent catalyst. Int. J. Miner. Process.80 (2), 261–265.

Park, K.-H., Kim, H.-I., Parhi, P., 2010. Recovery of molybdenum from spent catalystleach solutions by solvent extraction with LIX 84-I. Sep. Purif. Technol. 74 (3),294–299.

Petzold, G., Schwarz, S., 2013. Polyelectrolyte Complexes in Flocculation Applications,Polyelectrolyte Complexes in the Dispersed and Solid State II. Springer, pp. 25–65.

Sato, T., Watanabe, H., Suzuki, H., 1990. Liquid-liquid extraction of molybdenum (VI)from aqueous acid solutions by TBP and TOPO. Hydrometallurgy 23 (2–3), 297–308.

Sebenik, R.F., et al., 2002. Molybdenum and molybdenum compounds. In: Ullmann'sEncyclopedia of Industrial Chemistry.

Seo, S.Y., Choi, W.S., Yang, T.J., Kim, M.J., Tran, T., 2012. Recovery of rhenium andmolybdenum from a roaster fume scrubbing liquor by adsorption using activatedcarbon. Hydrometallurgy 129, 145–150.

Shalchian, H., et al., 2017. On the mechanism of molybdenite exfoliation during me-chanical milling. Ceram. Int. 43 (15), 12957–12967.

Shalchian, H., et al., 2018. An enhanced dissolution rate of molybdenite and variableactivation energy. Hydrometallurgy 175, 52–63.

Sharma, A.K., et al., 2018. Two dimensional α-MoO3-x nanoflakes as bare eye probe forhydrogen peroxide in biological fluids. Anal. Chim. Acta 1015, 58–65.

Su, L., et al., 2019. MoO3 nanosheet-assisted photochemical reduction synthesis of Aunanoparticles for surface-enhanced Raman scattering substrates. Sensors Actuators BChem. 279, 320–326.

Valdés, H., et al., 2009. Characterization of chemical kinetics in membrane-based li-quid–liquid extraction of molybdenum (VI) from aqueous solutions. Chem. Eng. J.151 (1), 333–341.

Van den Berg, J., Yang, Y., Nauta, H., Van Sandwijk, A., Reuter, M., 2002. Comprehensiveprocessing of low grade sulphidic molybdenum ores. Miner. Eng. 15 (11), 879–883.

Vizsolyi, A., Peters, E., 1980. Nitric acid leaching of molybdenite concentrates.

H. Shalchian, et al. Hydrometallurgy 190 (2019) 105167

10

Hydrometallurgy 6 (1), 103–119.Wang, M.-Y., Wang, X.-W., Jiang, C.-J., Tao, C.-F., 2014. Solvent extraction of mo-

lybdenum from acidic leach solution of Ni–Mo ore. Rare Metals 33 (1), 107–110.Warren, I., Reid, D., 1982. The recovery of molybdenum from leach solutions by reduc-

tion. Metall. Trans. B 13 (4), 565–570.Wu, J., et al., 2012. Selective extraction of Mo using Cyanex-272 and tributyl phosphate

from low grade Ni–Mo ore leach liquor. Sep. Purif. Technol. 99, 120–126.Zhao, Z., et al., 2010. Recovery and purification of molybdenum from Ni–Mo ore by direct

air oxidation in alkaline solution. Hydrometallurgy 103 (1), 68–73.Zhao, Z., Cao, C., Chen, X., Huo, G., 2011. Separation of macro amounts of tungsten and

molybdenum by selective precipitation. Hydrometallurgy 108 (3), 229–232.Zhong, M., et al., 2018. Highly anisotropic solar-blind UV photodetector based on large-

size two-dimensional α-MoO3 atomic crystals. 2D Materials 5 (3), 035033.Zhu, Z., Tulpatowicz, K., Pranolo, Y., Cheng, C.Y., 2015. Solvent extraction of mo-

lybdenum and vanadium from sulphate solutions with Cyphos IL 101.Hydrometallurgy 154, 72–77.

H. Shalchian, et al. Hydrometallurgy 190 (2019) 105167

11